As mentioned, not a low light lens but that's not what it's made to handle.

I bought the Tamron 18-250 as an "all around" lens for my 30D. On receiving it I was really surprised at the size and weight of it for a superzoom lens. In testing I found my copy to have excellent center sharpness across the whole focal length. Edge sharpness at 250mm is somewhat lacking if you "pixel peep" at 100%. Distortion at 18mm is well controlled and I have seen worse for sure.
To date there is one review on the net and I pretty much agree with most of his evaluation. Just "google" for reviews on it.
I also recently picked up a Pentax K10D and to be honest have been checking daily on the availability of the 18-250 for it. That should sum up my thoughts on the lens . Gerry